It's not just about pain relief, it's a "midwife knows best" and "nature knows best" doctrine. My experiences with midwives made me suspect two factors at play (though of course that doesn't mean they are the only two).
One is a general idea that "natural is best" and that therefore the ultimate birth to aim for is a drug-free vaginal birth. I think this is a hangover from the backlash against over-medicalised births several decades ago and I agree they were over-medicalised, but that doesn't mean natural, vaginal, midwife-led birth suits everyone. Some midwives cling to this like a dogma and that can turn into pressure.
The other is a kind of war between doctors and midwives where midwives will actively contradict and dismiss doctors' advice. Now that might be appropriate sometimes and I understand if more doctors are male and more midwives female they might feel that they understand more. But for some of us, medication and surgery are there for a reason and it's extremely alarming seeing them slip away from you.
I had a CS agreed by a consultant after a previous EMCS, but went into labour before the booked date. I was HEAVILY pressured by several midwives to try for a VBAC and if any probs "we can aways use forceps"
. A baby had died from incorrect use of forceps at that hospital not long before. And I already knew I needed a CS as I had a problem dilating and a large-headed baby. This was all on my notes. As was my history of sexual abuse and difficulty with internals. But the midwives' only priority seemed to be a natural birth, as if it was only fair to TRY for that because if I managed it I'd be happier. No, I wouldn't. I'd had a CS before, I needed a CS again and I didn't give a crap about "succeeding" at a VBAC.
The only reason IMO that I argued my case and got my CS is that I'm very assertive, articulate and stubborn. What if I didn't have good english, was easily cowed or had fallen prey to the idea that a CS is some kind of failing? It could have been disastrous.